First test ride is done. Ok, this one was easy, indoors on smart trainer, no changing weather conditions. I compared the output of my DIY power meter with the outputs of my Elite Kura smart trainer (claimed to be 1% accurate) as well as Garmin Vector 2s. 

I am quite confident that I am on the right track. This plot shows the raw ANT+ data, no smoothing applied:

Even short "sprints" are managed quite well:

But will this work outdoors? Currently, we have like -3° C outdoors, so it will be a difference of 25° C between the warm crank at start and freezed crank at the end of the ride. We will see...